Currently, salt content measurement in the crude oil production and refining industry follows either the standard reference method ASTM D3230 or ASTM D6470, both of which are incorporated herein by reference. ASTM D6470 is not practical for online measurement as it requires extraction steps. ASTM D3230 requires the utilization of a combination of three chemicals: methanol, butanol, and xylene, to reduce the crude oil resistivity to a measurable range for traditional sensors and common instrumentation. However, these solvents are extremely toxic, volatile, and flammable, which makes them particularly difficult to handle in facilities located in hot environments.
The principle of the method outlined in ASTM D3230 is to dilute a crude oil sample in an alcoholic mixture in order to allow for conductivity readings and to compare the readings to reference values. This method can be applied either off-line on a collected sample or online. Off-line measurements are susceptible to errors due to unequal gas desorption, which can be attributed to time lag between sampling and measurement and/or variations of the external temperature and/or the crude oil temperature, improper mix of chemicals, measurement errors, and data reporting. Online measurements avoid manual sampling and prevent some potential errors. However, in high temperature environments, the use of volatile solvents is inadvisable because it can lead to fires, explosions, or intoxication. Another disadvantage of ASTM D3230 is the limitation in solvent quantity stored on site due to flammability concerns and risks of explosion.
Furthermore, xylene, methanol, and butanol must be added in precise proportions, as any minimum alteration in their volumetric ratio, which is even more likely to occur at high temperatures due to their volatile nature, disturbs the homogeneity and causes erroneous measurement readings. This leads to a complicated measurement procedure, thereby introducing potential errors. Moreover, these issues also require bulky equipment with frequent and careful maintenance.
Currently, there are no effective, efficient, and easy to use online analyzers for monitoring salt content in treated crude. The available online salt-in-crude analyzers are generally expensive and require high maintenance, as well as the use of solvents, as required by the ASTM standards. The frequent replacements of chemicals and the presence of moving parts in the analyzer make the analyzer labor-intensive and requires constant maintenance. Currently available online nuclear and radioactive-based salt-in-crude analyzers also require high maintenance and provide unreliable measurement. Additionally, off-line monitoring requires laboratory sampling to monitor the PTB. However, it is very easy to miss the product specification based on the timing of sampling collections and using an off-line monitoring system.
Therefore, it would be beneficial to provide a method and apparatus that is capable of measuring the salt concentration online and also modifying operating conditions such that salt concentration is maintained.